U.S. patent number 5,285,581 [Application Number 07/785,276] was granted by the patent office on 1994-02-15 for method for drying waste materials.
This patent grant is currently assigned to Combustion Design Corporation. Invention is credited to David R. Walker.
United States Patent |
5,285,581 |
Walker |
February 15, 1994 |
Method for drying waste materials
Abstract
A dryer assembly dries waste materials to a predetermined
moisture level. The dryer includes a drum having an inlet where
waste materials and hot gasses are simultaneously introduced, and
an outlet where dried materials and hot vapors are transferred out
of the dryer. The drum presents a plurality of preheat baffles in
which the material is heated by but does not contact the gasses,
thereby avoiding premature combustion of the material. Baffle
sections located downstream of preheat baffles uniformly distribute
material downstream into a primary drying section of the drum,
where the material is mixed with the gasses to uniformly dry the
material to the predetermined moisture level. The primary drying
section includes alternating baffle sections which dry the material
and which recycle material that is not yet dried back into the
preceding baffle sections, respectively. The dryer can be readily
adapted to accommodate a wide variety of materials of widely
varying moisture levels by modifying the dwell times of the
material within individual dryer sections and/or by varying the
diameter of the dryer and the lengths of the individual dryer
sections.
Inventors: |
Walker; David R. (Clearwater,
FL) |
Assignee: |
Combustion Design Corporation
(Tampa, FL)
|
Family
ID: |
1239357 |
Appl.
No.: |
07/785,276 |
Filed: |
October 30, 1991 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
510421 |
Apr 18, 1990 |
5080581 |
|
|
|
Current U.S.
Class: |
34/500; 34/135;
34/136; 432/106 |
Current CPC
Class: |
F26B
3/00 (20130101); F26B 11/0477 (20130101); F26B
11/028 (20130101) |
Current International
Class: |
F26B
11/00 (20060101); F26B 11/02 (20060101); F26B
11/04 (20060101); F26B 3/00 (20060101); F26B
017/00 () |
Field of
Search: |
;34/60,17,135,136,137,138,26,28,29,27 ;432/106 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Bennett; Henry A.
Attorney, Agent or Firm: Foley & Lardner
Parent Case Text
This application is a division, of application Ser. No. 07/510,421,
filed Apr. 19, 1990 now U.S. Pat. No. 5,080,581.
Claims
What is claimed is:
1. A method of uniformly drying a moisture-laden material,
comprising the steps of:
(A) introducing hot gasses and said moisture-laden material into a
first longitudinal end of a dryer comprising a preheating portion
and a mixing portion; then
(B) conveying said material through said preheating portion such
that said material is heated by but is shielded from direct contact
with said gasses, thereby ensuring that said material is not
subject to combustion; then
(C) conveying said material through said mixing portion such that
said material is uniformly mixed with said gasses and is dried to a
predetermined moisture level; then
(D) conveying said material and said gasses out of a common outlet
formed in a second longitudinal end of said dryer.
2. The method of claim 1, wherein said step (C) comprises the step
of conveying said material through a drum-type conveyor presenting
a plurality of baffles which are adapted to mix said material while
conveying said material within said dryer.
3. A method of uniformly drying a moisture-laden material,
comprising the steps of:
(A) introducing hot gasses and said moisture-laden material into a
dryer comprising a preheating portion and a mixing portion;
then
(B) conveying said material through said preheating portion such
that said material is heated by but is shielded from direct contact
with said gasses, thereby ensuring that said material is not
subject to combustion; then
(C) conveying said material through said mixing portion such that
said material is uniformly mixed with said gasses and is dried to a
predetermined moisture level; then
(D) conveying said material out of an outlet of said dryer,
wherein said step (C) comprises the step of conveying said material
through a drum-type conveyor presenting a plurality of baffles
which are adapted to mix said material while conveying said
material within said dryer; and
wherein said step (B) comprises the step of uniformly feeding
material into said preheating portion, then enclosing said material
in cupping sections of baffles, located within said preheating
portion, to protect said material from said hot gasses, while
rapidly transferring any part of said material not enclosed in said
cupping sections into said mixing portion.
4. The method of claim 2, wherein said step (C) comprises the step
of grasping said material as it leaves said preheating portion and
releasing different portions thereof at different points in a given
rotation cycle of said drum, thereby uniformly distributing said
material into a succeeding baffle section.
5. A method of uniformly drying a moisture-laden material,
comprising the steps of:
(A) introducing hot gasses and said moisture-laden material into a
dryer comprising a preheating portion and a mixing portion;
then
(B) conveying said material through said preheating portion such
that said material is heated by but is shielded from direct contact
with said gasses, thereby ensuring that said material is not
subject to combustion; then
(C) conveying said material through said mixing portion such that
said material is uniformly mixed with said gasses and is dried to a
predetermined moisture level; then
(D) conveying said material out of an outlet of said dryer,
wherein said step (C) comprises the step of conveying said material
through a drum-type conveyor presenting a plurality of baffles
which are adapted to mix said material while conveying said
material within said dryer; and
wherein said step (C) comprises the steps of conveying said
material through a series of alternating first and second baffle
sections defining a primary drying section of said mixing portion
where said material is uniformly dried to said predetermined
level.
6. The method of claim 5, wherein said step of conveying said
material through said first baffle sections comprises the step of
retaining material in traps of polyhedral baffles until said
material retained in each trap is dry enough to be conveyed by a
flow of vapor through said dryer.
7. The method of claim 5, wherein said step of conveying said
material through said second baffle sections comprises the step of
recycling within said primary drying section a part of said
material that has not yet been dried to a predetermined moisture
level, thereby further to dry said part.
8. The method of claim 1, further comprising the step of adjusting
the dimensions of said dryer to dry a wide variety of
materials.
9. The method of claim 2, further comprising the step of adjusting
the diameter of the dryer drum to meet the needs of a particular
material.
10. The method of claim 2, further comprising the step of adjusting
the dimensions and numbers of said baffles to meet the drying needs
of a particular material.
11. A method of uniformly drying a moisture-laden material,
comprising the steps of:
(A) introducing hot gasses and said moisture-laden material into a
dryer comprising a preheating portion and a mixing portion, said
preheating portion comprising a plurality of baffles which are
constructed with cupping devices; then
(B) conveying said material through said preheating portion while
enclosing said material in said cupping devices of said baffles and
protecting said material from said hot gasses such that said
material is heated by but is shielded from direct contact with said
gasses, thereby ensuring that said material is not subject to
combustion; then
(C) conveying said material through said mixing portion such that
said material is uniformly mixed with said gasses and is dried to a
predetermined moisture level; then
(D) conveying said material out of an outlet of said dryer.
12. The method of claim 11, further comprising conveying said
gasses out of said outlet of said dryer.
13. The method of claim 12, wherein step (A) comprises introducing
said hot gasses and said moisture-laden material into a first
longitudinal end of said dryer; and
wherein step (D) comprises conveying said material and said gasses
out of a common outlet formed in a second longitudinal end of said
dryer.
14. The method of claim 13, wherein said step (D) comprises
carrying said material out of said common outlet of said dryer via
said gasses.
15. The method of claim 1, wherein said step (D) comprises carrying
said material out of said outlet of said dryer via said gasses.
16. The method of claim 11, further comprising, after step (D), the
steps of:
(E) receiving from said outlet a vapor stream laden with moisture
and particulate matter; and
(F) separating said particulate matter from said vapor stream.
17. The method of claim 16, wherein step (F) includes introducing
the vapor stream into a device for vapor clarification.
18. The method of claim 17, wherein step (F) further includes
separating said vapor stream into a primary stream containing
clarified vapor, and a secondary stream containing a relatively
high concentration of particulate matter.
19. The method of claim 18, further comprising, after step (F), the
step of:
(G) clarifying said secondary stream by introducing said secondary
stream into a separation cyclone and removing particulate
matter.
20. The method of claim 19, further comprising, after step (G), the
step of:
(H) returning said clarified secondary stream to said device and
further clarifying said clarified secondary stream into clarified
vapor.
21. The method of claim 20, further comprising, after step (H), the
step of:
(I) recycling said clarified vapor by introducing said clarified
vapor into said dryer, and by mixing said clarified vapor in a
mixing chamber with combustion gases from a furnace.
22. The method of claim 21, wherein step (I) includes removing a
moisture-laden vapor portion of said clarified vapor through an
exhaust stack.
23. The method of claim 21, wherein step (I) includes operating a
damper to limit a recycle rate and to ensure that said mixing
chamber is operating at less than atmospheric pressure.
24. The method of claim 1, further comprising, after step (D), the
steps of:
(E) receiving from said outlet a vapor stream laden with moisture
and particulate matter; and
(F) separating said particulate matter from said vapor stream.
25. The method of claim 24, wherein step (F) includes introducing
the vapor stream into a device for vapor clarification.
26. The method of claim 24, wherein step (F) further includes
separating said vapor stream into a primary stream containing
clarified vapor, and a secondary stream containing a relatively
high concentration of particulate matter.
27. The method of claim 24, further comprising, after step (F), the
step of:
(G) clarifying said secondary stream by introducing said secondary
stream into a separation cyclone and removing particulate
matter.
28. The method of claim 27, further comprising, after step (G), the
step of:
(H) returning said clarified secondary stream to said device and
further clarifying said clarified secondary stream into clarified
vapor.
29. The method of claim 28, further comprising, after step (H), the
step of:
(I) recycling said clarified vapor by introducing said clarified
vapor into said first longitudinal end of said dryer, and by mixing
said clarified vapor in a mixing chamber with combustion gases from
a furnace.
30. The method of claim 29, wherein step (I) includes removing a
moisture-laden vapor portion of said clarified vapor through an
exhaust stack.
31. The method of claim 29, wherein step (I) includes operating a
damper to limit a recycle rate and to ensure that said mixing
chamber is operating at less than atmospheric pressure.
Description
BACKGROUND OF THE INVENTION
The invention relates to a system for drying waste, mare
particularly to a system for drying a wide range of sludge and
other materials which vary in moisture content.
Environmental concerns have motivated a search for waste disposal
systems capable of disposing of waste materials in accordance with
the applicable regulating standards. The most widely used of these
disposal means comprises incinerating the waste materials. It has
ben discovered that incineration of such waste is most efficient if
the material is preconditioned through drying before it is
incinerated. However, conventional waste disposal systems
incinerate waste without drying or with only minimal drying. Those
systems that do dry waste materials typically include a dryer that
removes a portion of the liquids from the waste materials. For
example, U.S. Pat. No. 3,716,002 (Porter et al.) discloses a solid
waste disposal system in which high-moisture content wastes are
conveyed through a dryer where they are mixed with hot gasses
before they are incinerated. But in order to avoid pre-mature
combustion of the materials, the temperature of the gasses are not
high enough to completely dry the wastes, requiring the
recirculation of partially dried waste into the inlet of the dryer
to premix with wet incoming waste such that the mixture has a
reduced moisture content per unit weight of dryer throughput. This
system thus is inefficient in that only a fraction of the material
that is dried is actually passed on to the burner. Furthermore,
there are no means in the dryer to ensure that the wastes are
uniformly dried before they are conveyed to the burner.
Other conventional systems which dry waste materials are relatively
inefficient and are incapable of accommodating a wide range of
waste materials. To handle sludge materials having a high moisture
content, for example, conventional systems must consume an
excessive amount of fuel to uniformly dry high-moisture materials
to a level necessary for complete combustion, resulting in an
extremely inefficient drying operation. In addition, these systems
are inflexible because they must be individually designed to
dispose of a narrow range of waste materials. They are further
limited in their treatment of a particular material, e.g. sludge,
in that they burn prematurely (over-condition) materials of a
relatively low moisture level and fail to adequately dry materials
of a relatively high moisture level (under-conditioning).
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
dryer assembly which can be adapted easily to cleanly and
efficiently dry a wide range of waste materials having wide ranges
of moisture content, using a minimum amount of fossil fuels
uniformly to dry.
It is a further object of the invention to provide a method for
efficiently and uniformly drying a wide range of waste
materials.
In achieving the stated objects, the present invention provides for
a dryer assembly having an inlet portion, and outlet, and means for
conveying materials from the inlet portion to the outlet. The
conveying means includes pre-heating means, located within the
inlet portion, which heats the materials within a space in which
hot gasses are present but do not contact the material, such that
combustion of the material is avoided while the temperature of the
gasses is decreased. The conveying means further includes mixing
means, located in a mixing portion situated between the preheating
means and the outlet, which mixes the material with the gasses to
dry the material uniformly to a predetermined moisture level.
In accordance with another aspect of the invention, the conveyor
means comprises a drum type conveyor which presents a plurality of
baffles. These baffles are adapted to mix the material while
conveying it within the dryer.
In accordance with still another aspect of the invention, a
plurality of the baffles are located within the inlet portion and
are constructed with a cupping design which encloses the material
and protects it from the hot gasses. Each of these baffles also
includes external feed accelerators adapted to rapidly transfer a
portion of the material into the mixing portion.
In accordance with another aspect of the invention, a plurality of
the baffles in the mixing portion form alternating first and second
baffle sections which define a primary drying section where the
material is uniformly dried to the predetermined level. Each of the
first baffle sections has a plurality of support bars extending
radially inwardly form the perimeter of the drum and a plurality of
polyhedral baffles mounted on each support bar. Each of the second
baffle sections comprises a plurality of baffles having cupping
members adapted to recycle within the primary drying section a part
of the material that has not yet been dried to a predetermined
moisture level.
According to still anther aspect of the invention, a method is
provided for drying waste material which includes the steps of
introducing hot gasses and a moisture laden material into the dryer
which has a preconditioning and mixing portion, conveying the
material through the preconditioning portion such that the material
is heated by but does not contact the gasses, thereby avoiding
premature combustion of the material, conveying the material
through the mixing portion until it is uniformly mixed with the
gasses and is dried to predetermined moisture level and conveying
the material out of the outlet of the dryer.
According to yet another aspect of the invention, the method can
include the step of adjusting the dimensions of the dryer to dry a
wide variety of material having different moisture levels.
Other objects, features and advantages of the present invention
will become apparent from the following detailed description. It
should be understood, however, that the detailed description and
the specific examples, while indicating preferred embodiments of
the invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the
invention will become apparent to those skilled in the art from
this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a is a flow chart depicting a waste disposal system in which
drying according to the present invention is effected.
FIG. 1b is a flow chart depicting a belt press and waste heat
evaporator used in conjunction with the present invention to
prepare materials having an extremely high moisture content.
FIG. 1c is a flow chart depicting a scrubber system usable in
connection with an embodiment of the present invention.
FIG. 1d is a flow chart depicting the waste disposal system that
incorporates an embodiment of the present invention.
FIG. 2 is a side view of a waste disposal system including a
preferred embodiment of the present invention.
FIG. 3 is a top view of the waste disposal system.
FIG. 4 is an end view of the waste disposal system.
FIG. 5 is a front view of the burner in a preferred embodiment of
the present invention.
FIG. 6 is a sectional view of the burner of FIG. 5.
FIG. 7 is a partially schematic cross-sectional side view of a
preferred embodiment of the dryer assembly of the present
invention.
FIG. 8 is an perspective view of an end section of the feeder
baffle section of the dryer assembly of FIG. 1.
FIG. 9 is a sectional view taken along line a--a of FIG. 7.
FIG. 10 is a sectional view taken along line c--c of FIG. 7.
FIG. 11 is an enlarged view of a portion of FIG. 10
FIG. 12 is a sectional view taken along line d--d of FIG. 7.
FIG. 13 is an enlarged view of a portion of FIG. 12.
FIG. 14 is a sectional view taken along lines e--e of FIG. 7.
FIG. 15 is a sectional view of a portion of a fan assembly taken
along the line 15--15 in FIG. 3.
FIG. 16 is a top view of the fan assembly of FIG. 15.
FIG. 17 is a sectional side view of a fan used in connection with
the present invention.
FIG. 18 is a side view of the fan of FIG. 17.
FIG. 19 is a top view of the fan of FIG. 17.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Pursuant to the present invention, waste materials are uniformly
dried to a predetermined moisture level. This predetermined
moisture level may be, for example, a level at which effective
incineration can be performed. The dryer includes a drum having an
inlet where waste materials and hot gasses are simultaneously
introduced, and an outlet where dried materials and hot vapors are
transferred out of the dryer. The drum presents a plurality of
preheat baffles in which the material is heated by but does not
contact the gasses, thereby avoiding premature combustion of the
material. Baffle sections located downstream of the preheat baffles
uniformly distribute material downstream into the primary drying
section of the drum, where the material is mixed with the gasses to
uniformly dry the material to the predetermined moisture level. The
primary drying section includes alternating baffle sections which
dry the material and which recycle material that is not yet dried
back into the preceding baffle sections, respectively. The dryer
can be readily adapted to accommodate a wide variety of materials
of widely varying moisture levels by modifying the dwell times of
the material within individual dryer sections and/or by varying the
diameter of the dryer and the lengths of the individual dryer
sections.
The dryer of the present invention is preferably used in
conjunction with a system which conditions and incinerates waste
materials of widely varying moisture contents. A detailed
description of a preferred embodiment of the dryer assembly and of
a system into which the dryer can be incorporated follows.
With regard to boxes 1 and 2 in FIG. 1a, the first step in the
depicted process is to bring the material into the primary
treatment plant and prepare (precondition) the waste material to
ensure that it is at a suitable temperature and moisture level, and
is free from excess particulate matter, before entering the drying
process (box 3). This initial step can include, for example,
running the waste material through a belt press-type filter 5, or
any other type of mechanical dewatering device, and a scrubber 6 to
remove and sterilize any supernatant liquid prior to conveying the
waste material to the dryer.
In the embodiment shown in FIG. 1d, boxes 20-24, waste materials
that have a high metal content or otherwise require a higher
combustion temperature undergo primary treatment such as microwave
and ultra-sonic bombardment at station 22, such that the solid
waste particles are pre-conditioned enabling the waste particles to
liberate bound water when thermally activated thus improving the
efficiency of the system in producing the desired end point
moisture level.
As shown in FIG. 5, after the waste material has been
preconditioned in belt filter presses or other preconditioning
stages, raw feed auger 110 receives the wet waste material from the
belt filter presses and conveys it to dryer feed tube 111. Dryer
feed tube 111 is connected to recycle tube 112 which attaches to
the recycle conduit 106 at 113. Recycle gasses are thus push-pulled
through feed tube 111, cleaning the internal surface of the feed
tube and, thereby, avoiding particle buildup and eventual
stoppage.
As shown in FIGS. 2-4, preconditioned materials are conveyed into
the primary conditioning system at the feed entry 109. The primary
conditioning system includes a dryer assembly 200, a fan assembly
300 which removes vapors from the dryer outlet, and a burner 100
which gassifies in conjunction with incinerating the materials
exiting dryer 200 and mixes hot exhaust gasses with vapors
transported by fan assembly 300 to produce the hot gasses
constituting the drying media for the dryer 200.
The burner is used to gassify and incinerate the waste material
after it is uniformly dried. Thermal disposal of the waste in this
manner also generates energy which can be used in part in drying
the sludge during the preconditioning stage. As noted above, the
exhaust gasses from the burner 100 are mixed with vapors recycled
from the fan assembly 300 to produce a gas which is of a
temperature suitable for drying the material.
Many types of furnaces can accomplish the thermal disposal
function. It is desirable to use a furnace that employs a type of
burner that effects complete combustion of even high moisture
content fuels by providing, as needed, both primary and secondary
incineration. Exemplary of this type of burner is the so-called
"vortex gassifier combuster" (VGC) described in U.S. Pat. No.
4,574,711 (J. Vernon Christian), the contents of which are hereby
incorporated by reference. The control circuit for the VGC includes
thermosensitive means which establish a set point temperature for
the furnace, measures the flue gas and furnace temperature and
controls the delivery of fuel and combustion air to the combustion
chamber of the VGC to ensure that the set point temperature is
maintained thereby ensuring efficient combustion which reduces
pollution and prevents excess fuel consumption. The set point
temperature can be adjusted depending on the type of waste material
to be gassified and incinerated in the VGC. Exemplary of this type
of control circuit is the so-called "stokermaster" control circuit
described in U.S. Pat. No. 4,517,902 (J. Vernon Christian), the
contents of which are hereby incorporated hereto by reference. This
system takes into account the control parameters which affect
efficient incineration of solid fuels, and calculates and maintains
a set-point temperature at which the most efficient operation of a
solid fuel burner is achieved.
In FIG. 5, component 100 is a VGC burner. After leaving the dryer,
waste which has been dried to the predetermined moisture level
enters the primary combustion chamber 101 of burner 100 at points
A, B, or C or in any combination of these points. The hot flue gas
(1600.degree.-2300.degree. F.) generated from the primary
combustion of the waste material passes into a secondary combustion
chamber 102 where the flue gas may be mixed, if further combustion
is required, with flue gas generated from an auxiliary gas/oil
burner 103. The heated flue gas then travels to a mixing chamber
104, where a two-step cooling process occurs. First, a combination
of water vapor from the waste material and cooler vapor drawn from
dryer exhaust conduit 105 mixes with hot flue gas from the VGC
burner. The cooler vapor can have a temperature between
165.degree.-275.degree. F., for example, although a higher
temperature may be appropriate, depending on the type of waste
material. Mixing of the cooler vapor and hot flue gas forms gasses
which enter a feed entry conduit of the dryer at a desirably
reduced temperature range, for example, in a range of
600.degree.-1400.degree. F. Any excess flue gas which is not
recycled to the mixing chamber is conveyed to discharge conduit 107
where oxidation of volatile materials takes place before the gas is
discharged to the atmosphere.
Since the gasses are still too hot to come into direct contact with
the waste material, recycle conduit 106 conveys the cooler recycled
gasses from the fans to the feed entry conduit 109. The cooler
recycled gasses then mix with the hot gasses from the mixing
chamber to ensure that the gasses which enter the dryer 200 are at
a lower temperature more suitable for drying the waste material.
Recycle conduit 106 includes a damper 108 which limits the amount
of cooler recycled gasses conveyed through recycle conduit 106,
thereby ensuring that mixing chamber 104 is operating at
less-than-atmospheric pressure, for example, around -0.25" W.C.,
thereby creating a partial vacuum. This negative pressure in mixing
chamber 104 prevents hot gasses from escaping through conduit 107
to the atmosphere, thereby ensuring that the maximum amount of hot
gasses are recycled, thus enhancing the overall efficiency of the
VGC burner.
In addition, the control circuit of the VGC discussed earlier also
contains thermosensitive circuits which control the temperature of
the gasses recycled through the dryer. The thermosensitive circuits
measure the temperature of the dryer exhaust vapor in conduits 106
and 107 and adjust the amount of fuel being incinerated by the VGC
to control the moisture level of the vapor which ultimately
controls the temperature of the flue gasses which mix with the
cooler vapor for recycling through the dryer.
With reference to FIG. 7, the high-moisture waste materials are
conveyed through an inlet 201, of the dryer assembly 200 into a
rotating dryer drum 202 where they are uniformly dried to a
predetermined moisture level before leaving the dryer assembly at
exit 203. The heat for drying the materials is supplied by the hot
gasses which are produced by the furnace 100 and which also enter
the dryer 200 at inlet 201. The dryer drum includes a feeder baffle
section 204 which controls the feed rate of materials into the
remaining dryer sections, a baffle section 210 in which the
materials are preheated to achieve a more efficient drying
operation, a distribution baffle section 220 which evenly
distributes materials into the succeeding baffle sections, and a
primary drying section comprising a plurality of heat transfer
baffle sections 230 and recycle baffle sections 240. An outlet cone
250 is located at the outlet 203 of the dryer assembly.
As shown in FIG. 8, the feeder baffle section 204 is fitted with a
plurality of paired infeed feeder vanes 205 which function to
control the feed rate of materials to be dried to the inside of the
baffle section 210. These paired vanes function to limit the amount
of material fed into the baffle section 210 by cupping an optimal
amount of material within the paired vanes 205 required for proper
operation of the succeeding baffle sections. When material is fed
into the dryer at a higher rate than the baffle section 210 can
accommodate, the result is a back-up of materials in the paired
feeder vanes 205, and the excess materials spill over the cup
formed by the feeder vanes. When the flow rate of materials into
the dryer decreases, the excess materials is again cupped by the
feeder vanes and fed to the baffle section 210. This operation
ensures that material volume is evenly distributed throughout the
dryer, effecting a more uniform drying operation.
A system of the present invention can be adapted to condition
different materials by varying the number of infeed baffles
installed in a given drum radius. The number of baffles to be
installed will depend on the moisture level of the materials being
conditioned, the percentage of combustible elements in the
materials, and the adhesion coefficient of the materials on the
baffles 205. For example, inbound materials containing 83% moisture
and having a small coefficient of adhesion would require 36
baffles, covering 1% of the dryer length, and materials containing
25% moisture and having a high coefficient of adhesion would
require 20 baffles covering 10% of the dryer length. The size of
the drum 202 can be varied in proportion to the volume of material
that is to be conditioned in a given time period.
Materials exiting the feeder baffle section 204 are conveyed into
the baffle section 210 where they are preheated to a temperature at
which efficient drying can be performed. The materials are
preheated in this section by the combination of indirect heat
transfer from the hot gasses and the heat from the surface area of
the baffle sections. With reference to FIG. 9, the individual
baffles of the section 210 are constructed with a cupping design
211 to enclose the materials and to protect them from the hot
furnace gasses flowing through the center of the drum. This cupping
action is necessary in light of the fact that the gasses entering
the drum are generally hot enough to burn materials on contact.
Such a premature combustion of the materials would create
undesirable air-borne particulates. But the heat transfer which
takes place within this section cools the gasses leaving the
section to a point where they can contact the materials without
effecting combustion.
These baffles 210 each have external feed accelerators 212 for
rapidly transferring to the next section any materials that bypass
the feeder baffle section or that cannot be accommodated by the
cupping design due to a temporary overload condition. These
accelerators 212 rapidly pass the materials to the downstream
baffles without dropping them through the hot gasses.
The number of baffles in the baffle section 210 will be varied as a
function of the heat transfer properties of the waste materials,
the amount of combustibles in the materials, the amount of
preheating needed to release water in succeeding dryer sections,
the flow rate of material into the dryer assembly, and drum size,
among other variables. For example, with the drum sized for an
appropriate throughput, waste materials having a 25% moisture level
and an ambient temperature of 75.degree. F., would require 12
baffles and a preheat section of 18% of the dryer length.
As shown in FIG. 7, the materials exiting baffle section 210 next
enter distribution baffle section 220, which functions to evenly
distribute materials into the downstream heat transfer baffle
section 230. This section includes a plurality of lifter baffles
designed to distribute the materials uniformly through the hot
gasses and onto the heat transfer baffles 230. In FIG. 10, the
lifter baffles 221, 222, 223, of each distribution baffle section
220 extend radially from the outer perimeter of the drum and are of
three progressively increasing angles which release the materials
at different points in a given rotation cycle of the drum 202. Air
circulation within the drum then evenly distributes the materials
into the next section 230 for heat transfer with the hot gasses,
thereby ensuring a more uniform drying operation. The lifting and
dropping action of these baffles 221, 222, 223 also functions to
break apart any large clumps of material before they enter the
first of the heat transfer sections 230.
The length of the baffle section 210 can be varied by changing the
number of baffle sections placed in the distribution section. For
example, materials having an inbound moisture level of 83% and a
medium coefficient of adhesion would require a distribution baffle
section covering 38% of the dryer length. Materials having an
inbound moisture level of 83% and a low coefficient of adhesion
would require a distribution baffle section covering 25% of the
dryer length. It is desirable to vary the length of this section in
dependence on material properties to provide optimum distribution
of materials. For example, because a primary purpose of this
section is to expose the materials to sufficient air flow to move
them to the next section and to break up any aggregated product,
the length of the distribution baffle section 220 will have to be
increased as the density and/or the volume of material
increases.
The materials exiting the distribution baffle section 220 in FIG. 7
are uniformly distributed onto the first baffle section of a
primary drying section in which the materials are uniformly dried
to the predetermined moisture level. The primary drying section
includes a series of alternating heat transfer baffle sections 230
and recycle baffle sections 240. The last heat transfer baffle
section 230 opens into the dryer drum exit 203 via velocity cone
250. The construction and function of one of each of the individual
baffle sections 230 and 240 will be discussed in detail below.
The heat transfer baffle sections 230 are designed to provide
uniform drying of materials. Each section includes a plurality of
baffles specifically designed for high heat recovery from the hot
gasses produced by the furnace. It should be noted that the hot
gasses exiting the dryer assembly are properly categorized as
vapors, since they have absorbed substantial amounts of moisture
from the materials by the time they exit the last of the baffle
sections.
As shown in FIGS. 12 and 13, each of these heat transfer baffle
sections 230 comprise a plurality of alternating primary and
secondary baffle support bars 231 and 232 extending radially
inwardly from the outer perimeter of the drum and a plurality of
polyhedral baffles 235 supported on each support bar. To maintain
sufficient baffle surface to cross sectional areas at all portions
of the drum diameter, the lengths of the secondary support bars 232
are approximately one half that of the primary support bars 231.
Each of the support bars is attached on a flat bar backup plate
233. This backup plate also serves to suppress the flow of gasses
through the dryer to maintain gas flow rates at the desired level.
A deflector cone 234 is located at the center of the baffle section
230 to suppress further the flow of gasses through the dryer.
The support bars 231 and 232 form right angle baffles, and the
polyhedral baffles 235 each have traps 236, 237 and 238, which
extend at respective angles of 60, 70 and 90 degrees from the
support bars on which they are attached. The traps 236, 237, and
238 enclose the materials so as to form miniature "drums" in which
the material in each trap is independently dried via heat
transferred from the metal surface of the traps of the material and
also via direct transfer from the vapors to the material. Clearance
between the individual traps of each polyhedral baffle 235 and the
corresponding right-angle baffle formed by the corresponding
support bar 231 or 232 is designed to retain materials in each
baffle section 230 until they are light enough to be moved by the
vapor stream. This section also functions to break apart any
aggregations of materials to increase material quality and to
improve heat exchange efficiency.
The length of the individual baffle sections 230 can be varied
based on the amount of energy required to evaporate the moisture in
the materials to the predetermined level. Factors which influence
the required length of the respective baffle sections include the
temperature of the materials entering the section, the amount of
surface contact between the hot gasses and the material, the heat
exchange coefficient of the materials, and the ability of the
baffles to break apart the materials and the resulting surface area
of the materials. The required length of these sections will also
vary with the moisture content of the inbound materials, which will
vary with dryer drum size.
With reference again to FIG. 7, materials exiting the first of the
heat transfer baffle sections 230 enter the first recycle baffle
section 240. This baffle section 240 assures that the materials are
uniformly dried by injecting high density materials, which are not
yet dry enough to be conveyed by the gas flow, back into the first
heat transfer baffle section 230 for further drying. The recycle
baffle section 240 comprises a plurality of inverted return or
back-step baffles, one of which is shown in FIG. 14. Each of these
baffles comprise a 180 degree cup 241 on the dryer centerline side
of the baffle section 240 to hold the materials during drum
rotation and to shield the flow of materials which are being
recycled from the dryer gas stream. The cup 241 is also tapered at
a 30 degree angle to provide reverse acceleration of materials back
into the first heat transfer baffle section 230. A deflector cone
242 is located at the center of the baffle section 240 to maintain
gas flow rates at the desired level.
The angle of attack of the inverted baffles for each section 240
and their distance from the outer drum shell of each recycle baffle
section 240 are matched to drum rotation velocity and material
specific gravity. These variables determine the amount of reverse
flow of materials that is required and, thus select the moisture
content of the materials which leave the baffle section 240. The
length of the individual baffle sections 240 can be varied in
dependence on the size of the dryer drum, which, as previously
mentioned, varies with the volume of material to be
conditioned.
The materials continue to travel from section to section where they
are progressively dried until they reach the velocity cone 250,
located at the center of the exit 203 of the drum 202, which
controls the flow rate of exiting materials and insures that only
dried materials exit the dryer assembly. The velocity cone 250 has
a 5 to 1 base to altitude ratio to reduce the air velocity through
the open cone section, thereby controlling the flow rate of the dry
materials. It also deflects any small sized particles that are
being carried by the vapor stream back into the heat transfer
baffle section 230. This ensures that material exiting the dryer
assembly is carried by the vapor flow by virtue of its low specific
gravity, brought about by a low moisture content, rather than
simply its small particle size. The velocity cone 250 thus provides
a final assurance that all of the materials exiting the dryer
assembly 200 have reached the predetermined moisture level.
By changing the numbers of alternating heat transfer baffle
sections 230 and recycle baffle sections 240, the dryer 200 can be
readily modified to dry a variety of materials to different
moisture levels. In addition, the amount of preheating performed in
baffle section 210 and material distribution performed in section
220 is modifiable simply by changing the number of baffle sections
210 and 220. In addition, the individual baffle sections can be
replaced by sections specifically designed for a given application,
the design considerations for which were discussed above. A given
dryer assembly thus can be quickly and easily modified to perform a
wide variety of drying and conditioning operations.
In FIGS. 2-5, dried materials exiting dryer 200 are conveyed to
furnace 100 via a conveyor 315, where they are incinerated as
discussed above. The conveyor also communicates with the fan
assembly 300, which withdraws the vapors from the dryer and
clarifies and recycles the vapors.
Both the hot gasses used to dry the waste material and the
particulate emissions from the dryer discharge stack preferably
satisfy applicable air quality regulations relating to federal air
regulation standards. Accordingly, recycling/separating fans shown
generally at 300 (see FIGS. 3, 4 and 17-19) are attached to an
outlet duct 290 of the dryer assembly 200. These fans are
multi-purpose in that they draw hot, moisture-laden vapor through
the dryer assembly, separate the particulate contamination from
this vapor stream, and pump the cleaned, recycled vapor stream back
to the VGC burner via dryer exhaust conduit 105 and recycle conduit
106 (FIG. 5). Although various types of dust control/fan systems
can accomplish the recycling/separating function a preferred dust
control system is used which accelerates incoming vapor streams to
centrifugally separate particulate matter from the vapor stream.
Because the fans are operating at the same temperature as the dryer
exhaust vapor, there is no condensation and no accumulation of
water vapor. The fans thus assure that vapor entering exhaust stack
107 (FIGS. 2 and 3) is free of condensed water.
As shown in FIGS. 16 and 17, suction box 301 is the focal point of
the dust control system. The Magnum Fans 400 are located in the
roof of the suction box 301 (see FIG. 16). The number of fans is
determined by the drying capacity of the dryer. A detailed
description of the fan structure will follow. The hot vapors
withdrawn from the dryer are subjected to a two-tier clarification
process before being recycled.
As shown in FIGS. 15-17, each of the Magnum Fans 400 is situated on
top of suction box 301 to allow the suction box to lower the
velocity of the vapor so that heavier material in the dryer drum
falls out of the vapor stream, to be removed by primary evacuating
auger 315 (see FIG. 3). Each fan 400 includes a conical shaped
inlet portion 401 which tapers towards the outlet thereof which
communicates with impeller inlet 404. The conical shape of this
inlet portion 401 increases the velocity of the incoming vapor
stream to a level sufficient to centrifugally remove heavier
particulate matter from the stream while preventing the collection
of particulate matter on the sides or bottom of the inlet portion
401.
The suction box 301 is designed for supporting the load of the fans
400, to support and enclose primary cyclones 305, and to support
exterior secondary cyclones 305'. The secondary cyclones 305' are
used in systems that require more stream clarification than can be
achieved by the interior primary cyclones 305. By enclosing the
primary cyclones 305 within the suction box 301, the temperature of
the vapor entering the cyclones remains hot, thereby preventing a
temperature differential that would lead to condensation. Such
condensation is undesirable, as particulate matter in the vapor
stream would adhere to the condensed moisture on the internal
surfaces of the system. This particulate matter would at least
partially block the internal ducts of the system, thus reducing its
operational efficiency. The amount of condensation in the secondary
cyclones 305' is also reduced by placing the fans on top of the
suction box 301 which ensures that the vapor stream entering
cyclones 305' from fans 400 is of a relatively high temperature.
The structure and operation of the fan assembly and suction box,
including the cyclones, will now be described with reference to
FIGS. 15-19.
First, as illustrated by FIG. 16, the internal dust collection
system of the suction box accelerates the vapor withdrawn from the
dryer assembly and separates the vapor into a primary stream of
clarified media and a secondary stream, the latter containing a
high concentration of particulate matter. The primary stream which
contains the clarified vapor is conveyed out of the fan to conduits
105 and 106. The secondary stream is discharged into conduit 303.
Conduit 303 serves as a common manifold and leads to the entrance
304 of high-efficiency cyclone collectors 305. The number of
cyclone collectors in each system can be varied in accordance with
the type of waste material being processed. The suction box 301
includes louvers 320, located on top of the suction box adjacent
the fans, which control the velocity of the vapor stream, to cause
fall-out of the large sized waste particulates removed from the
dryer drum. These louvers are designed based on the consistency of
the material being processed. The angle and coverage of the louvers
will be changed to match material specifications.
Cyclones 305 and 305' further clarify the entering secondary stream
by decelerating the secondary stream and causing the remaining
particulate matter to fall to the lower portion 306 of the cyclones
(FIG. 15). As seen in FIG. 15, the fallen particulate matter then
exits the cyclones 305 at point 307 and enters a common auger
conveyor 308. To maintain an effective a seal at cyclone exit 307
into conveyor 308, the auger employs a full pitch auger 309.
Without the seal on the bottom of the auger, some of the inbound
vapor is lost through the bottom of the cyclone. Such a loss of
vapor would result in a reduced volume, and thus a reduced
velocity, of vapor in the cyclone, lowering the efficiency of the
particulate removal operation. Thus, auger speed is regulated to
maintain a particulate control level 311 in the up stream cyclone
exit 307. Outside air is prevented from entering the negative
pressure in the system by a positive seal created by the
particulate matter itself and controlled by the speed of auger
309.
The clarified secondary stream now returns to the suction box 301
via conduit 313 (FIGS. 15 and 16). Any particulate matter remaining
in the secondary stream is immediately recycled through the fans
400 as illustrated in FIGS. 15 and 16 where the above noted dust
collecting cycle is repeated. The clarified secondary stream is
then discharged from the fan assembly 300 and is conveyed to the
front of the dryer assembly 200 via conduits 105 and 106. If
desired, a portion of the vapors removed by fan assembly 300 can be
supplied to the waste heat evaporator 6 via stack 107 (FIG. 1b-3)
to perform the evaporation and scrubber operation.
A more detailed description of the internal dust collection system
of one of the fans 400 follows. As shown in FIG. 17, vapor heavily
laden with particulate matter is drawn into the fan entry 401 from
the interior of suction box 301 and is conveyed in a converging
nozzle 402 toward a Vortex breaker baffle 403 at the impeller inlet
404. As seen in FIGS. 17-19, an impeller 405 has several inclined
blades 405' which extend away from the direction of rotation of the
fan at an angle of 30 degrees from the exterior circumference of
the fan. The impeller 405 imparts axial energy to the vapor and
particulate matter, directing the vapor and particulate matter to
enter a series of accelerating chambers 406, mounted at about a
60.degree. angle around the inside perimeter of the fan casing 407.
The chambers 406 accelerate the vapor through a downwardly
spiralling (centrifugal) motion. The vapor then leaves the
accelerating chamber and enters separating chambers 408 (FIG. 17).
The particulate matter is thus accelerated in chambers 406 and is
then separated from the vapor by adhering to the inner fan casing
wall 407. The downward spiraling vortex motion (centrifugal motion)
thus produced by the chambers 406 conveys the vapor and particulate
matter, now highly separated, through the separating chamber 408
and into the concentrating area 409. The concentrating area formed
by the inner fan casing wall 407 and the converging cone 402 acts
to re-accelerate the concentrated vapor and particulate matter.
This re-acceleration ensures that the particulate matter will have
sufficient momentum to impact tangentially against an inner scroll
casing wall 410 of the fan 400. The inner and lower portion of the
scroll wall form a conduit with a directing vane 411 attached to
the scroll wall 407. The directing vane 411 has a vertical leg
which traps particulate matter in the conduit formed by the scroll
wall 410 and vane 411. The conduit conveys particulate matter to
the particulate exit 412.
The directing vane 411 also forms an annulus with fan casing 407.
This annulus allows the clarified vapor to enter passageway 413.
Passageway 413 becomes a conduit formed by scroll casing 410 and
fan casing 407 whereby clarified vapor is conveyed to the fan
clarified vapor exit 414.
The funnel for the particulate matter exit 412 begins at point 415
and ends at the exit 412. Point 415 is also the beginning of the
inclined transition plate 416 that directs clarified vapor to the
fan clarified vapor exit 414.
* * * * *